Pachypodium lamrei (Madagascar Palm)

Pachypodium - Pachypodium spp.

Pachypodium is a genus of succulent spine-bearing trees and shrubs, native to Africa. It is a genus of about 20 to 24 species and belongs to the large family, Apocynaceae. Like all species in this family - Pachypodium's sap is poisonous to stock/human. Pachypodium comes from Greek pachy (thick) and podium (foot), hence meaning thick-footed, referring to the thickened stem or caudex.

The majority are from Madagascar  with some from southern Africa. The usually bottle-shaped trunk is usually solitary and wide, they range from small (eg P. brevicaule), to six to ten metres tall 'trees' (eg P. lamerii and P. geayi) and armed with stout paired spines and topped with a rosette of long leaves (sort of palm-like ... hence the common name 'Madagascar Palm' for some species). They flower on mature plants, that might be 10 years or more from seed, and like most members of the Apocynaceae family they are large and showy.

Genus characteristics
All Pachypodium are succulent plants that exhibit, to varying degrees, the morphological characteristics of pachycaule trunks and spinescence. These are the most general features of the genus and can be considered distinguishing characteristics.

The pachycaule trunk is a morphologically enlarged trunk that stores water so as to survive seasonal drought or intermittent periods of root desiccation in exposed, dry, and rocky conditions. Whereas there is great variation in the habit of the plant body, all Pachypodium exhibit pachycaul growth. Variation in habit can range from dwarf flattened plants to bottle shaped shrubs to dendroid-shaped trees.

The second general characteristic of Pachypodium is spinescence, or having spines. The spines come clustered in either pairs or triplets with these clusters often arranged in rings or whorls around the trunk. Spines emerge with leaves, and like leaves grow for a short period before stopping growth and hardening. Spines do not regenerate so weathering and abrasion can wear away all but the youngest spines from older specimens - leaving smooth trunks and branches.

To some extent, branches are a characteristic of the genus. Some caution is warranted in over-generalizing this characteristic. Pachypodium namaquanum is often branchless. Pachypodium brevicaule has no clear branches, and indeed may have evolved an alternative to branching in the form of nodes from which leaves, spines, and inflorescences emerge. In general Pachypodium have few branches. Since the environmental stresses and factors that contribute to branching can vary widely even in small areas, individual plants of the same species exhibit wide variation in branching morphology.

Unlike many members of the Apocynaceae, including some members of the superficially similar Adenium, Pachypodium species do not exude a milky latex. Rather, the sap is always clear.

Madagascar Palm (Pachypodium lamerei) is a species of Pachypodium. It has large thorns and leaves mostly just at the top of the plant. It is a stem succulent and comes from the island Madagascar. The plant bears large, fragrant flowers. The species has become one of the best known pachypodiums in cultivation, being relatively easy to propagate and grow. In cultivation it is often marketed as the "Madagascar Palm", despite in not being a palm at all. A variety called "Ramosum" has been described. It is distinguished mostly by a dwarf growth habit.

Pachypodium lamerei has a tall, silvery-gray trunk covered with sharp 6.25 cm spines. Long, narrow leaves grow only at the top of the trunk, like a palm tree. It rarely branches. Although plants grown outdoors will reach up to 6 m, when grown indoors, it will slowly reach 1.2-1.8 m tall.

Plants grown outdoors will develop large, white, fragrant flowers at the top of the plant. However, it rarely flowers indoors.

Source:
http://en.wikipedia.org/wiki/Pachypodium
http://en.wikipedia.org/wiki/Pachypodium_lamerei
http://pachypodium.net/
http://www.cssnz.org/pachypodium-and-caudiciforms.php